Signalling circuit



March 13, 1956 J. A. DOREMUS 2,733,455

SIGNALLING CIRCUIT Filed March 26, 1953 Fig. 1 I EL. a

IN V EN TOR.

John A Doremus BY United States Patent SIGNALLING CIRCUIT John A. Doremus, Chicago, Ill., assignor to Motorola, Inc., Chicago, Ill., a corporation of Iilinois Application March 26, 1953, Serial No. 344,774

12 Claims. (Cl. 3201) This invention relates generally to signalling circuits and more particularly to selective circuits which discriminate against undesired signals of short duration such as noise.

In selective signalling equipment it is desired in many applications to cause operation of certain controls when a particular signal has been received. Such systems may be frequency responsive so that they are operated only by a signal of a particular frequency. However, random signals such as noise may include the particular frequency, and it is therefore necessary to cause the systems to be time responsive as well so that operation does not take place until the particular signal has been received for a predetermined length of time.

In such selective systems a condenser is often used as the time responsive element with the system being rendered operative when a certain voltage is built up across the condenser. The amplitude of this voltage depends upon the time that the signal is applied, but unfortunately the charging curve of a condenser has a relatively steep initial rise so that a relatively large voltage is built up in a very short period of time. Further, some time is required to discharge the condenser so that a plurality of signals in rapid succession may cause the voltage to add up to the required value and therefore improperly trip the system. Although the use of an inductance would provide the desired voltage build-up characteristic, indoctors are relatively expensive and are therefore objectionable. It is therefore an object of this invention to provide an improved selective responsive system.

It is another object of the present invention to provide an improved selective responsive system which is substantially unresponsive for a predetermined time interval to thereby discriminate against undesired signals such as noise.

A further object of this invention is to provide a signal responsive system wherein the effective charge on a condenser is modified so that the voltage developed thereacross has a slow initial rise and a rapid rise thereafter.

A feature of this invention is the provision of a signalling circuit including condenser means charged by signals of a predetermined frequency, and including means for providing a counteracting voltage of short duration so that the overall voltage remains substantially zero for a predetermined time and then rises rapidly when the countervoltage ceases.

Another feature of this invention is the provision of a selective circuit including condenser means to which the signal is applied and means applying a countervoltage to the condenser means including differentiating means and phase inverting means. The differentiating means to provide the voltage pulse at the initiation of a signal may be formed by a condenser and a resistor, with the voltage pulse across the resistor being applied to a tube which reverses the phase thereof. Alternatively, the differentiation and phase reversal may both be provided by a transformer to thereby eliminate the need for additional tubes.

2,738,455 Patented Mar. 13, 1956 Further objects, features and the attending advantages of the invention will be apparent from a consideration of the following description when taken in connection with the accompanying drawings, in which:

Fig. 1 illustrates a standard selecting circuit using the charge on a condenser as the selecting quantity;

Fig. 2 is a plurality of curves illustrating the operation of the system of Fig. 1;

Fig. 3 illustrates one embodiment of the improved circuit in accordance with the invention;

Fig. 4 is a plurality of curves illustrating the operation of the system of Fig. 3; and

Figs. 5 and 6 are alternative embodiments of the system in accordance with the invention.

In practicing the invention there is provided a selective signalling system wherein a selected signal is applied to a condenser to charge the same to cause a desired operation when the voltage across the condenser reaches a predetermined value. To render the system unresponsive to signals of short duration which may repeat to thereby cause a considerable charge across the condenser, a circuit is provided to produce a countervoltage pulse which is combined with the voltage across the condenser. The countervoltage pulse is of short duration so that it cancels the voltage developed across the condenser during the initial period of the signal, but has substantially no effect thereon after a predetermined time, so that the system responds to signals of a duration greater than the predetermined time. The countervoltage may be provided by a circuit including differentiating and inverting means. This maybe in the form of a condenserresistor differentiating circuit and a vacuum tube acting as an inverter, or by a transformer which provides both the differentiation and inversion of the signal.

Referring now to the drawings, in Fig. 1 there is illustrated a selecting signalling system which is of known construction. This system includes input terminals 10 and 11 to which a signal may be applied. The terminals are connected to an electromechanical responsive device such as the vibrating reed structure 12. The reed structure 12 may be tuned to a particular frequency so that when a signal of this frequency is received the reed will vibrate to cause intermittent closing of the contacts 13 thereof. This will provide a closed circuit from the plus potential through resistor 14 and condenser 15 to charge the condenser 15. Resistor 16 is connected in parallel across condenser 15 to discharge the same. The voltage development across condenser 15 may be applied to the grid 17 of the tube 18 which includes a relay 19 in the cathode circuit thereof. When the voltage across condenser 15 reaches a predetermined value, it will cause the tube 18 to conduct and the relay 19 will close to cause a desired operation.

The operation of the system of Fig. l is illustrated in Fig. 2. Curve A illustrates the voltage developed across the condenser 15 when a signal of the desired frequency is applied to the terminals 10 and 11. It will be noted that as the signal is applied to the condenser 15, the voltage rises rapidly at first and then levels off so that it remains practically constant. The tube 18 may be biased so that it conducts when the signal is applied for the time ti, and the voltage reaches the value indicated by the dot-dash line B. When the signal is no longer applied, the voltage across the condenser 15 will discharge through resistor 16 as indicated by the portion of the curve marked C.

As shown by curve D, the voltage across the condenser 15 may be brought to a value suificient to cause the tube 18 to conduct by intermittent pulses each of which is not of sufficient length to individually cause operation of the system. The curve D rises in response to the first signal which is of a duration t2. When the signal ceases,

the voltage across the condenser will start to drop but if another signal of the same frequency comes along, the voltage will again rise and if this signal has a duration of time is as shown, the curve D will reach the level B which causes the tube 18 to conduct. This will result in a false operation of the system.

In Fig. 3 there is illustrated an improved circuit in accordance with the invention wherein discrimination is provided against operation of the system by short duration signals of the desired frequency. This circuit includes input terminals 20 and 21 connected to electromechanical responsive device 22 which may be of the same type as the device 12 of Fig. 1. This includes contacts 23 which are intermittently closed when a signal of a particular frequency is applied to the input terminals 20 and 21. Closing of the contacts 23 applies the positive potential across two paths, the first including resistor 24 and condensers 25 and 26. This operation tends to charge the condensers 25 and 26 to the potential of the plus source.

The voltage of the plus source is also applied to a second path including condenser 27 and resistor 28. The condenser 27 and the resistor 28 are selected to have such values that the condenser 27 will charge rapidly and therefore a pulse of voltage will be developed across the resistor 28 during the charging of the condenser 27. In other words, this is a difierentiating circuit. The voltage across resistor 28 is applied to tube 30, being applied to the grid 31 thereof. The cathode of this tube is connected to ground through a self-biasing circuit including resistor 32 and condenser 33. The plate of the tube is connected to B+ through resistor 34 and is also connected to the intermediate terminal between condensers 25 and 26. The voltage pulse developed across resistor 28 will be inverted and amplified by the tube 30 and will be developed across the condenser 26.

A resistor 35 is provided bridged across condensers 25 and 26 to discharge the same. The voltage across condensers 25 and 26 is applied to a tube 36 which functions in the same manner as the tube 18'- of Fig. 1. This tube may include a relay 37 in the cathode circuit thereof which is rendered operative when the tube conducts a predetermined amount.

For a consideration of the operation of the circuit of Fig. 3 reference is made to Fig. 4. In Fig. 4 curve B illustrates the voltage developed across condenser 25 because of the charge developed by the current flowing through resistor 24. This curve is identical to the curve A of Fig. 2.' Curve F illustrates the voltage developed across resistor 28 and this voltage is a short pulse, the duration of which depends upon the values of condenser 27 and resistor 28. This pulse which is applied to the triode 30 causes an output voltage wave as shown by curve G, and this is developed across condenser 26. The curve G will be substantially equal and opposite to the curve F depending upon the amplification of the tube 30 and the value of condenser 26.

The voltage across condenser 26 is combined with the voltage across condenser 25 so that the voltage at the grid of the tube 36 will be the sum of the two volt ages which has a shape as shown by the heavy curve H m Fig. 4. It will be seen that this curve has a very slow use so that short duration signals will have no effect on the system. However, after a predetermined time the curve rises sharply so that signals of longer duratron will cause the voltage to reach the value required to cause the tube 36 to conduct and render the relay 37 operative.

In Fig. 5 there is illustrated a second embodiment of the invention wherein the countervoltage is produced by the differentiation and inverting action of a transformer. g'. 5 the input is applied. to termials' 40 and 41 which are connected to a selective responsive electromechanrcal device 42. The application to the electromechanrcal device of signals of'the desired frequency causes the contacts 43 thereof to intermittently contact to provide a closed circuit from the positive potential through resistor 44 to condensers 45 and 46 to charge the same.

The positive potential is also applied across the primary winding 47 of a transformer, the secondary 48 of which is connected to the intermediate terminal between condensers 45 and 46. The windings 47 and 48 are so phased that the increasing current through the winding 47 produces a voltage pulse across the winding '48 which charges the condenser 46 negatively for a short time as the positive potential is applied to the Winding 47. This produces a voltage pulse across condenser 46 generally as shown by curve G of Fig. 4 and this combines with curve E which is developed across condenser 45 to provide a voltage at the grid of tube 47 which has the general configuration of curve H of Fig. 4. This curve has the desired slow initial rise and then rises rapidly to reach the value which causes the tube 47 to conduct. This will render the system non-responsive to undesired pulses of short duration such as noise pulses.

In Fig. 6 there is illustrated a further embodiment in which the countervoltage is produced by a transformer. In this circuit signals are applied to the input terminals 5 and 51 of the electromechanical device 52 to cause intermittent closing of the contacts 53 thereof. This applies the positive potential through primary winding 54 and resistor 55 to condensers 56 and 57 to charge the same. Resistors 61 and 62 are connected across the condensers for discharging the same. The increase of current through the Winding 54 induces a voltage pulse in the winding 58 which is applied through rectifier 59 to charge the condenser 57. This produces an initial pulse across condenser 57 in response to the increase of current through the winding 54 as the condenser 56 begins to charge. The rectifier 58 is phased to produce a negative pulse across condenser 57 which counteracts the initial rise of the voltage developed across condenser 56 to provide a voltage at the grid of the tube 60 similar to the curve H of Fig. 4. The rectifier 59 prevents the positive pulse which is formed when the current through winding 54 reduces and results in very sharp action discrimination against short pulses.

It is therefore seen that a circuit has been provided which discriminates against signals of short duration. The

length of signals which are not effective may be controlled by controlling the constants of the circuit. Therefore the system can discriminate against recurring pulses of short duration. The system is such that signals which are only a little longer than the duration which is not effective, will cause operation of the system.

The system is believed to be suitable for use in many applications, and although illustrated in a frequency responsive system, it is to be pointed out that the application of the invention is not limited to such systems. Further, the means for providing the countervoltage may be of various different constructions and is not limited to the particular circuits illustrated. It is intended to cover all such variations of the circuit which come within the spirit of the invention and the scope of the appended claims.

I claim:

1. A. selective responsive system including in combination. condenser means, means connected to said condenser means for applying signals thereto to produce a first voltage thereacross, means for providing a voltage pulse in response to the initial application of a signal to said condenser means, and means for applying said voltage pulse to said condenser means so that said voltage pulse opposes said first voltage and the combined voltage has a slow initial rate of rise and then rises relatively rapidly.

2. A selective responsive system including in combination, condenser means, circuit means connected to said condenser means for applying signals thereto to pro- .duce a first voltage thereacross, difierentiating means Connected to said circuit means for providing a voltage pulse in response to the initial application of a signal to said condenser means, inverter means for reversing the phase of said voltage pulse, and means for applying said inverted voltage pulse to said condenser means so that said voltage pulse tends to cancel the initial rise of said first voltage and the combined voltage has a slow initial rate of rise and then rises relatively rapidly.

3. A selective responsive system including in combination, signal supplying means, means connected to said supplying means across which a first voltage is developed which increases with the duration of the signal supplied, pulse producing means coupled to said signal supplying means for providing a short voltage pulse in response to the initial application of a signal thereto, and means for combining said first voltage and said voltage pulse so that said voltage pulse opposes said first voltage and the combined voltage has a slow rate of rise for the duration of said pulse and then rises rapidly.

4. A selective responsive system including in combination, condenser means, means connected to said condenser means for applying signals thereto to produce a first voltage thereacross, means for diiferentiating and inverting said signal to provide a voltage pulse of opposite polarity to the voltage across said condenser means in response to the initial application of a signal to said condenser means, and means for applying said voltage pulse to said condenser means so that said voltage pulse opposes said first voltage and the combined voltage has a slow initial rate of rise and then rises relatively rapidly.

5. A selective responsive system including in combination, condenser means, circuit means connected to said condenser means for applying signals thereto to charge said condenser means and produce a first voltage wave thereacross, and resistor means connected to said condenser means for discharging the same, said circuit means including a portion providing a voltage pulse in response to the initiation of a signal, said circuit means applying said voltage pulse to said condenser means so that said voltage pulse opposes said first voltage wave to produce a second combined voltage wave having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval.

6. A selective responsive system including in combination condenser means, circuit means connected to said condenser means for applying signals thereto to charge the same and produce a first voltage wave thereacross, and

resistor means connected to said condenser means for dischar ing the same, said circuit means including a differentiating portion providing a voltage pulse in response to the initiation of a signal, and an amplifier portion for inverting the voltage pulse and applying the same to said condenser means, said condenser means combining said first voltage wave and said voltage pulse so that said voltage pulse opposes said first voltage wave to produce a second combined voltage Wave having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval.

7. A selective control system including in combination condenser means, circuit means connected to said condenser means for applying signals thereto to charge the same and produce a first voltage wave thereacross, resistor means connected to said condenser means for discharging the same, said circuit means including a differentiating portion providing a voltage pulse in response to the initiation of a signal, and an amplifier portion for inverting the voltage pulse and applying the same to said condenser means, said condenser means combining said first voltage Wave and said voltage pulse so that said voltage pulse opposes said first voltage wave to produce a second com bined voltage wave having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval, and control means connected to said condenser means for providing a control operation when said second combined voltage wave reaches a predetermined value.

8. A selective responsive system including in combination, condenser means, frequency selective means connected to said condenser means for intermittently applying a voltage thereto in response to a signal of a predetermined frequency to charge said condenser means and produce a first voltage wave thereacross, resistor means connected to said condenser means for discharging the same, circuit means connected to said frequency selective means including a differentiating portion providing a voltage pulse in response to the initiation of a signal and an amplifier portion for inverting the voltage pulse and applying the same to said condenser means, said condenser means combining said first voltage wave and said voltage pulse so that said voltage pulse opposes said first voltage wave to produce a second combined voltage wave having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval, and control means connected to said condenser means for providing a control operation when said second combined voltage wave reaches a predetermined value.

9. A selective responsive system including in combination, condenser means, frequency selective means connected to said condenser means for intermittently applying a voltage thereto in response to a signal of a predetermined frequency to charge said condenser means and produce a first voltage thereacross, resistor means connected to said condenser means for discharging the same, circuit means connected to said frequency selective means including means for differentiating and inverting the voltage applied to said condenser means to produce a voltage pulse of opposite polarity to said first voltage, said circuit means being connected to said condenser means and applying said voltage pulse thereto, said condenser means combining said first voltage and said voltage pulse so that said voltage pulse opposes said first voltage to produce a second combined voltage having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval, and control means connected to said condenser means for providing a control operation when said second combined voltage reaches a predetermined value.

10. A selective responsive system including in combination, condenser means, frequency selective means connected to said condenser means for intermittently applying a voltage thereto in response to a signal of a predetermined frequency to charge said condenser means and produce a first voltage thereacross, resistor means connected to said condenser means for discharging the same, and circuit means connected to said frequency selective means for differentiating and converting the voltage applied thereby to produce a voltage pulse of opposite polarity to said first voltage, said circuit means being connected to said condenser means for applying said voltage pulse thereto, said condenser means combining said first voltage and said voltage pulse so that said voltage pulse opposes said first voltage to produce a second combined voltage having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval.

11. A selective responsive system including in combination condenser means, circuit means connected to said condenser means for applying signals thereto to charge the same and produce a first voltage thereacross, and resistor means connected to said condenser means for discharging the same, said circuit means including a transformer to which the signal is applied for providing a voltage pulse in response to the initiation of a signal, said transformer being connected to said condenser means and applying said voltage pulse thereto in a polarity opposite to that of said first voltage so that said voltage pulse tends to initially cancel said first voltage to produce a second combined voltage having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval.

12. A selective control system including in combination condenser means, circuit means connected to said condenser means for applying signals thereto to charge the same and produce a first voltage thereacros's, and resistor means connected to said condenser means for discharging the same, said circuit means including a transformer to which the signal is applied for providing a voltage pulse in response to the initiation of a signal, said circuit means including rectifier means connecting said transformer to said condenser means and applying thereto only said voltage pulse of a polarity opposite to that of said first 10 1 8 voltage so that said voltage pulse tends to initially cancel said first voltage to produce a second combined voltage having a slow initial rate of rise and a relatively rapid rate of rise after a predetermined time interval.

References Cited in the file of this patent UNITED STATES PATENTS 

